I have a Cooper Model 22 in 257 Roberts that may have an issue. I bought the rifle used a couple years ago. The issue is when I resize the fired brass the last half inch takes a lot of force to size the base. I notice a slight bulge at the web of the fired brass. I measured the base with a mic. Before firing it measures .466 after firing it measure .473. Fired cases extract fine. I did a comparison to a 30-06 I have, on that one, resized measured .465 and fired measured .469. Also I'm noticing that the 257 brass is growing in length and having to trim more often. It seems to expand on even new brass after the first firing. I never load to max and keep all loads well below the max. I don't know the history of this rifle or what kind of loads were put through it. What could cause this and is it a problem? Is it time for a new barrel? All opinions appreciated. Thanks.
Possible chamber issue.
- Thread starter kleanbore 1
- Start date
jackieschmidt
Gold $$ Contributor
Your chamber is a little large at the web. Repeated firings will work the brass a little harder, is this a problem, probably not as long as you limit the number of firings on each individual case. Common sense dictates that a larger dimensional change from firing to sizing tp firing does work the brass more
Is this really a problem. I see brass laying at our local gun club that has a very noticeable bulge at the web. All probably fired from various Factory chambers.
If this is a limited use hunter, don’t worry about it. If you are sitting at the bench all day shooting on the same 15 cases, maybe that’s a problem.
Using a good sizing wax such as Imperial will help with the resizing.
Is this really a problem. I see brass laying at our local gun club that has a very noticeable bulge at the web. All probably fired from various Factory chambers.
If this is a limited use hunter, don’t worry about it. If you are sitting at the bench all day shooting on the same 15 cases, maybe that’s a problem.
Using a good sizing wax such as Imperial will help with the resizing.
jepp2
Gold $$ Contributor
Several questions.
1. First how well does it shoot currently? The reason I ask, is I have 2 Cooper M-22 and the accuracy is excellent. Last thing I would want to do is rebarrel one of them.
2. I don't know your sizing practices and how much you set the shoulder back from the fired length. I am not necessarily and advocate for neck sizing only, and normally neck size and set the shoulder back just enough so I have 0.001" clearance from bolt contact. BUT, in your case since you are working the case head area a lot, maybe trying just neck sizing for a few firings might be helpful.
3. The relatively shallow shoulder angle of the 257 Roberts can results in more material being removed during trimming after sizing. The move you move the shoulder, the more the case is going to stretch.
If your accuracy is good, you can buy a lot of brass and get less loadings for what a new barrel is going to cost installed. If your throat is good, replacing the barrel would not be my first option.
L.Sherm
Silver $$ Contributor
Its not overly big at the web saami is .4722 and I think they allow .001 either way.
It could be your die is sizing small at the web, you may call other die company's and ask them what there die sizes to at the web. .007 is alot im surprised you can size gown that far somewhere in the neighborhood of .469-470 probably would be better.
As the brass work hardens its gonna get tougher down at the web trying to size that much.
It could be your die is sizing small at the web, you may call other die company's and ask them what there die sizes to at the web. .007 is alot im surprised you can size gown that far somewhere in the neighborhood of .469-470 probably would be better.
As the brass work hardens its gonna get tougher down at the web trying to size that much.
If I am interpreting your post correctly, the problem is difficulty in F/L sizing and need to "frequently" trim cases even at below max loadings. How frequent?
No compliant on accuracy or functionality of the rifle with the reloads. Correct?
1. Before I would change anything, I would try Imperial Sizing Wax. In my experience, this is the best-case lube ever created. You need to know how to apply to get good results.
2. I would get a Sinclair chamber length gauge and measure the actual chamber length. This device is inexpensive and easy to use. You may not need to trim your cases anywhere near as much as you are doing now if you are basing your need to trim on SAMMI max case length specs.
What are the fired versus the sized case head space measurements? Are you extruding the case? Are you sizing too much? These measurements will tell you. Measure at least 5 cases.
If your F/L dies is not touching the shoulder you could be extruding (lengthening) the case. If you are bumping the shoulder back too much (> .003 bump), you could be creating excessive case stretch.
Since neither of the posted problems is creating an accuracy or functionality problem with the rifle, I would not re-barrel just so I could obtain easy sizing or to reduce the amount of trimming. If the above fixes don't satisfy you, then just carefully inspect cases after firing and sizing for any anomalies. Cases are a lot cheaper than barrels.
Also, given the caliber of this rifle, this appears to be a rifle used for hunting, not extensive range shooting. Therefore, perhaps you are looking for a solution to a problem that does not exist for the intended application of the rifle. A 50-round bag of brass would probably last you a hunting lifetime.
No compliant on accuracy or functionality of the rifle with the reloads. Correct?
1. Before I would change anything, I would try Imperial Sizing Wax. In my experience, this is the best-case lube ever created. You need to know how to apply to get good results.
2. I would get a Sinclair chamber length gauge and measure the actual chamber length. This device is inexpensive and easy to use. You may not need to trim your cases anywhere near as much as you are doing now if you are basing your need to trim on SAMMI max case length specs.
What are the fired versus the sized case head space measurements? Are you extruding the case? Are you sizing too much? These measurements will tell you. Measure at least 5 cases.
If your F/L dies is not touching the shoulder you could be extruding (lengthening) the case. If you are bumping the shoulder back too much (> .003 bump), you could be creating excessive case stretch.
Since neither of the posted problems is creating an accuracy or functionality problem with the rifle, I would not re-barrel just so I could obtain easy sizing or to reduce the amount of trimming. If the above fixes don't satisfy you, then just carefully inspect cases after firing and sizing for any anomalies. Cases are a lot cheaper than barrels.
Also, given the caliber of this rifle, this appears to be a rifle used for hunting, not extensive range shooting. Therefore, perhaps you are looking for a solution to a problem that does not exist for the intended application of the rifle. A 50-round bag of brass would probably last you a hunting lifetime.
The rifle does function fine, however the accuracy has never been what I expected from a cooper. 3/4 to 1" groups with an occasional flyer. That may not be related to the chamber issue though. I know coopers usually shoot much better. I have a model 54 Montana Varmiter in 6mm that shoots under 1/2 inch. I have hunted with the 257 but mostly shoot at targets. I like to shoot groups 1/2 inch or under, and can't seem to fine the load that will do that. I am only bumping the shoulder .002. I will order a sinclair chamber length gauge in .25 cal. I have them in several calibers but not 25. I should invest in a bore scope I guess to see what it looks like.
I will call a couple die companies and get their specs. The dies i'm using are old RCBS dies. I also like the idea of a neck size die. Thanks for all the suggestions.
I will call a couple die companies and get their specs. The dies i'm using are old RCBS dies. I also like the idea of a neck size die. Thanks for all the suggestions.
https://saami.org/ Appears normal, if looking at SAAMII specs.
WSnyder
Silver $$ Contributor
+.002" diameter on the chamber.
47WillysGuy
Gold $$ Contributor
Looking at Saami Specs for that area is0.4722, I’d say oversized chamber. Just over!
The Saami specs on head end of the case is 0.4711.
You’re squeezing the cases to 0.466 on head end. Your die could be considered “small base”. Your diameters should be more inline with the -06.
I would try a different die, your existing is too tight. IMHO! Good luck!
L.Sherm
Silver $$ Contributor
If you read up on saami im pretty sure they have an allowance and I believe its .001 either way.
If his measuring is .466 sized im more inclined to say its a die problem, to small
L.Sherm
Silver $$ Contributor
That will only make your sizing at the web worse as time goes, eventually you have to FL size brass hass a memory.
The correct FL die is the answer.
47WillysGuy
Gold $$ Contributor
I checked that dimension in Saami and they give no plus or minus on the head end. Of course’s the reamer manufacturer will get it close to 0.4722. His + or -.
My fired cases average 0.4704 ish. And size down to 0.4698 ish. About 1/2 thousand of an inch.
He needs a different die. Or he will be fighting the case sizing issue or wind up with a case head separation.
You can bend a wire so many times, then it breaks.
DaveTooley
Gold $$ Contributor
From SAAMI
Chamber
"Unless otherwise noted all dia. +.002"
I'll add every, and I mean every chamber yields a bulged case. It's necessary for expansion and contraction to get the case out of the chamber. That gets into matching the FL die to the chamber if it's a target rifle being reloaded on a regular basis. For a hunting rifle, I would use more lube on the body and move on. Ideal no, but as long I was getting the accuracy I wanted I wouldn't worry about it.
Chamber
"Unless otherwise noted all dia. +.002"
I'll add every, and I mean every chamber yields a bulged case. It's necessary for expansion and contraction to get the case out of the chamber. That gets into matching the FL die to the chamber if it's a target rifle being reloaded on a regular basis. For a hunting rifle, I would use more lube on the body and move on. Ideal no, but as long I was getting the accuracy I wanted I wouldn't worry about it.
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WSnyder
Silver $$ Contributor
With a +.002” tolerance that number is .4742”.
What print are you looking at? It clearly states +.002” on diameter and +.015” on length.
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swd
Silver $$ Contributor
I barreled a 30/06 years ago and the client brought it back for case bulging. The immediate thought was the chamber came out oversized. When we measured everything out the best we could it was pretty much in spec. So that lead us to looking at brass. I had access to a huge ammo collection and we started measuring 30/06 ammo from different eras and manufacturers and what we found was surprising to say the least. We saw up to .010” in case dimensions at the head. Even the same brand from different eras had huge variances.
A quick search for 257 chamber specs looks like most are .472”-473”. So if your virgin brass is .466” my strong suspicion is like 30/06, 257 Robert’s brass has changed a lot over the 100 years it’s been around.
If it were my rifle I would polish the back half of the die to size .002” at the .200” line and call it good.
A quick search for 257 chamber specs looks like most are .472”-473”. So if your virgin brass is .466” my strong suspicion is like 30/06, 257 Robert’s brass has changed a lot over the 100 years it’s been around.
If it were my rifle I would polish the back half of the die to size .002” at the .200” line and call it good.
dellet
Gold $$ Contributor
Cartridge and case drawings are minimum chamber, maximum cartridge. Then maximum allowances are defined on the side of the drawing.
Here maximum cartridge is .4711” -.008” for a minimum of .4631”.
Minimum chamber .4722” +.002” for maximum .4742”
Allowing for spring back after firing and sizing. Looks like near maximum diameter on the chamber, and minimum on the sizing die.m
Probably not all that uncommon
Here maximum cartridge is .4711” -.008” for a minimum of .4631”.
Minimum chamber .4722” +.002” for maximum .4742”
Allowing for spring back after firing and sizing. Looks like near maximum diameter on the chamber, and minimum on the sizing die.m
Probably not all that uncommon
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